This application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2004-275713 filed in Japan on Sep. 22, 2004, and on Patent Application No. 2004-299329, filed in Japan on Oct. 13, 2004, the entire contents of which are hereby incorporated by reference.
The present invention relates to optical discharge apparatuses for removing residual electric charges on photosensitive bodies by irradiating light, and to image forming apparatuses such as copier machines provided with same, in electrographic image forming processes.
As electrographic image forming apparatuses such as copier machines, there exist monochrome image forming apparatuses for forming black and white images, and color image forming apparatuses for forming color images. For color image forming apparatuses, there are multi-rotational image forming apparatuses for sequentially forming a toner image of composite colors onto a single photoreceptor via toner image forming means for each color (black, cyan, magenta and yellow), and tandem-type image forming apparatuses in which a plurality of toner forming means that form, substantially simultaneously, a toner image of the color components onto individual photosensitive bodies, are aligned along the transport direction of an intermediate transfer material.
Such electrographic image forming apparatuses are apparatuses that form images by the processes of charging, exposing, developing, transferring and fixing, and in the case of copier machines for example, the aforementioned processes are performed in the following manner.
First, an electrostatic latent image is formed on the surface of a photoreceptor (a photosensitive drum) that has been given a uniform potential by an electrostatic charger, by exposing the light reflected from the original image via an optical system. Toner (developer) is then electrostatically fixed to the electrostatic latent image to form a toner image on the photoreceptor. Next, an electrostatic charge having a polarity that is opposite to that of the toner image is applied to the transferring body so as to transfer the toner image onto recording paper, and an image according to the original image is fixed onto the recording paper by applying heat and pressure to the transferred toner.
A large number of functional elements are added to the basic configuration of a copier machine that is constituted as above, for the purpose of improving image quality and improving the efficiency of the facsimile image formation. One such element, for example, is an optical discharge apparatus for charge removal an electric charge on a photoreceptor using irradiating light. Optical discharge apparatuses include devices such as an eraser for erasing poor latent images from a non-image region on the photoreceptor before developing, a pre-transfer charge removal lamp (PTL) that optically reduces the electric potential on the photoreceptor before transfer, and a charge removal lamp (QL) for removing the residual charge on the photoreceptor after cleaning.
Electrical discharge tubes such as fluorescent tubes are used as the illuminating source for such optical discharge apparatuses. Furthermore, as shown in FIG. 29, an LED array 500 in which a plurality of LED chip 502 is arranged on a substrate 501 may be used. In particular, since smaller, cheaper products have been in demand in recent years, there has been an increase in the number of devices making use of this type of LED array 500.
As shown in FIG. 30, the LED array 500 is densely arranged with rows of LED chips (LED lamps) 502 so that it is possible to achieve a substantially uniform, high degree of illumination on the surface of a photosensitive drum 401, which is the illuminated surface.
However, with this configuration, since the number of LED ships 502 is large, it has been difficult to achieve sufficient reductions in cost. Also, when the number of LED chips that are used is decreased in order to achieve lower costs, the interval between LED chips 502 increases, inconsistencies have developed in the distribution of the illumination on the photosensitive drum 401. Thus it has not been possible to achieve a consistent degree of illumination.
As a technique to solve such problems, an illuminating device has been disclosed that is provided with a light source on an end portion of a light guiding member, the light guiding member having a light illuminating face that is a column-shaped member made from a transparent material that is provided with a side face portion extending in the long direction, and a light diffusing portion made by cutting or surface roughening, provided on a surface that opposes the light illuminating portion (See JP H8-043633A, for example).
Furthermore, an optical discharge apparatus is proposed that is provided with a point light source that is provided on a main body of an image forming apparatus, and an optical guiding body for guiding light from the point light source to the photoreceptor, mounted on a process cartridge that can be freely coupled and uncoupled to and from the main body of the image forming apparatus (see JP 2002-278395A, for example).
However, with the configurations described in aforementioned patent references, there still remains the problem that, of those regions of the photosensitive drum that are illuminated by the light from the optical guiding body, more light illuminates the regions closer to the light source, and less light illuminates those regions that are further removed from the light source. When there are inconsistencies in the distribution of the amount of illuminating light in the length direction of such a photosensitive drum, image inconsistencies and the like may occur, and it may be impossible to achieve a good image. In particular, in the vicinity of the trailing edge portion of the optical guiding body, which is furthest from the light source, there is a large degree of loss of illuminating light, and there is a need for improvement of this point.
The present invention has been achieved with consideration to such facts, and it is an object of the present invention to provide, in an electrographic image forming apparatus, an optical discharge apparatus that is capable of providing a more uniform distribution of light that is irradiated onto a photoreceptor to remove an electric charge on the photoreceptor, and to provide an image forming apparatus that is provided with an optical discharge apparatus that has such characteristics.